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Replaced loop with memcpys

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CPestka 2024-01-31 00:46:47 +01:00 committed by Andrew Kelley
parent 51d67c7c8f
commit 0c725a354a
1 changed files with 18 additions and 13 deletions
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31
lib/std/os/linux/io_uring.zig
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@ -268,29 +268,34 @@ pub const IO_Uring = struct {
/// See https://github.com/axboe/liburing/issues/103#issuecomment-686665007.
/// Matches the implementation of io_uring_peek_batch_cqe() in liburing, but supports waiting.
pub fn copy_cqes(self: *IO_Uring, cqes: []linux.io_uring_cqe, wait_nr: u32) !u32 {
const count = self.copy_cqes_ready(cqes, wait_nr);
const count = self.copy_cqes_ready(cqes);
if (count > 0) return count;
if (self.cq_ring_needs_flush() or wait_nr > 0) {
_ = try self.enter(0, wait_nr, linux.IORING_ENTER_GETEVENTS);
return self.copy_cqes_ready(cqes, wait_nr);
return self.copy_cqes_ready(cqes);
}
return 0;
}
fn copy_cqes_ready(self: *IO_Uring, cqes: []linux.io_uring_cqe, wait_nr: u32) u32 {
_ = wait_nr;
fn copy_cqes_ready(self: *IO_Uring, cqes: []linux.io_uring_cqe) u32 {
const ready = self.cq_ready();
const count = @min(cqes.len, ready);
var head = self.cq.head.*;
const tail = head +% count;
// TODO Optimize this by using 1 or 2 memcpy's (if the tail wraps) rather than a loop.
var i: usize = 0;
// Do not use "less-than" operator since head and tail may wrap:
while (head != tail) {
cqes[i] = self.cq.cqes[head & self.cq.mask]; // Copy struct by value.
head +%= 1;
i += 1;
const head = self.cq.head.* & self.cq.mask;
const tail = (self.cq.head.* +% count) & self.cq.mask;
if (head <= tail) {
// head behind tail -> no wrapping
@memcpy(cqes[0..count], self.cq.cqes[head..tail]);
} else {
// head in front of tail -> buffer wraps
const two_copies_required: bool = self.cq.cqes.len - head < count;
const amount_to_copy_in_first = if (two_copies_required) self.cq.cqes.len - head else count;
@memcpy(cqes[0..amount_to_copy_in_first], self.cq.cqes[head .. head + amount_to_copy_in_first]);
if (two_copies_required) {
@memcpy(cqes[amount_to_copy_in_first..count], self.cq.cqes[0..tail]);
}
}
self.cq_advance(count);
return count;
}